The invention relates to a process and an apparatus for the treatment of moist, explosive gas-dust mixtures, particularly coal dust mixtures in mill drying plants.
In processes of this type, which are well known in blast furnace and coalfired power station technology and which are described hereinafter in exemplified manner by means of the conditioning of moist raw coal to air-coal dust mixtures, it has hitherto been conventional practice to use a flue gas flow. The mills used in milling the moist raw coal are flowed through during the mill drying process by flue gas and hot process gas. As a result of this flue gas flow, a large part of the moisture in the raw coal is evaporated, so that the flue gas blown into the mill can be simultaneously used as a conveying medium for the coal dust mixture through the pipes and following dust collectors.
As frequently different capacities are encountered in the milling process in mills and the subsequent combustion of the coal dust mixture, the coal dust is discharged from the mill drying plant following the dust collectors and is intermediately stored in silos or storage bins.
In order to prevent coal dust explosions, deflagrations, etc. during the transportation of the coal dust mixture or during the intermediate storage of the coal dust, use is made of an injection of cold inert gas in such a way that explosive mixture formation is avoided.
However, longer transportation paths for the coal dust mixture, also within the framework of the flue gas flow, as well as the supply of cold inert gas in the following phases such as e.g. intermediate storage, lead to the temperature of the dust mixture or dust in a silo dropping below the dew point temperature of steam and consequently there is condensation of the residual moisture in the dust mixture or dust.
Even this condensation of residual moisture, frequently leads to agglomerations of the coal dust, which in turn leads to problems during the discharge of the coal dust mixture by means of the gas flow. As a result deposits can form in the pipe system and in particular blockages can occur in injection nozzles via which the coal dust mixture is e.g. supplied into the burners of blast furnaces.
In particular when storing coal dust in bins, such a condensation occurs in the cooler areas, so that a head or top heating, such as is frequently carried out, in the upper region of the storage bin fails to obviate this problem.